Optical communications involves imprinting or encoding information on light, thereby adapting the light to carry or convey the information as the light propagates or travels between two sites. The two sites may be across the globe or across a country, a state, a town, or a room, for example.
Imprinting or encoding information on the light typically involves modulating or changing some attribute or aspect of the light over time to create a pattern representing the information. A sender or transmitter of the information imposes the pattern on the light, and a receiver of the information identifies the pattern and thereby recovers the information.
For example, sailors on two distant ships may communicate with one another with powerful flashlights. One sailor pulses light on and off in a sequential pattern that represents letters of the alphabet, forming words and sentences, for example in Morse code. The other, distant sailor watches the light and notes the on-off pattern. Knowing the on-off sequences of each letter, that distant observer sailor determines the letters, words, and sentences via reversing the code. While modern fiber optic communication systems are more sophisticated than sailors sending messages to one another with flashlights, the basic concept is generally analogous.
A fiber optic communication system may comprise terminals or users linked together via optical paths, for example in a fiber optic network. Each terminal may comprise a transmitter and a receiver that may be components of a transceiver. Each terminal's transmitter typically outputs light imprinted or encoded with information destined for receipt at another, remote terminal. Meanwhile, each terminal's receiver typically receives light that has been imprinted or encoded with information at another, remote terminal. Accordingly, devices on an optical network can communication with one another via sending and receiving optical signals.
In one type of conventional approach, the outgoing light has one color or wavelength, and the incoming light has another color or wavelength. Thus, the transmitter includes a laser outputting optical signals of one color, which could be termed the “output color.” The transmitter may also include a monitor detector receiving a small sample of the outgoing optical signals to facilitate power control. That is, the laser may have an associated monitor detector for monitoring and controlling laser power or performance. When situated opposite a rear facet of a semiconductor laser, such a monitor detector can be termed a “rear facet monitor.” Meanwhile, the terminal's receiver includes a different detector receiving optical signals of another color, which could be termed the “input color.” The receiver detector is distinct and separate from the monitor detector, and the input color and the output color are distinct.
A system of one or more optical filters manipulates the incoming light and the outgoing light according to color. A typical optical filter implementation passes or transmits one color while reflecting another color, for example transmitting the output color and reflecting the input color. Such a filter can be positioned in the path of the light output by the laser, with the filter tilted at an angle to that path. In this configuration, the output laser light passes through the filter and onto the fiber optic network. The filter reflects the incoming light. By virtue of the filter being oriented at an angle relative to the light path of the output laser light, the reflected incoming light diverts to the detector of the receiver for receipt. In other words, the filter transmits the output light to the fiber optic network and diverts the incoming light (from the fiber optic network) to the receiver detector. Any incoming photons that might transmit through the filter and into the laser as stray light are generally inadvertent and unwanted. Accordingly, signal separation occurs in the optical domain.
One issue with the conventional transceiver technology described above concerns the optical filter. With many conventional optical filter technologies, filters can be more expensive than applications with tight cost constraints can tolerate. Moreover, conventional filtering systems often comprise lens systems for manipulating the filtered light. Such lens systems can be too expensive for cost-sensitive applications, such as fiber-to-the-home (“FTTH”), local area networks (“LANs”), optical buses within computing systems, backplane interconnects, core-to-core networks of microprocessors, etc., for which optical communications would be desirable at appropriate price points. In addition to expense issues, optical architectures of conventional transceivers often are not conducive to mass production. The constraints of aligning and assembling conventional filters and lenses usually call for special assembly techniques and equipment that are far more costly and less scalable than the technology available for electronic assembly. Finally, most conventional transceivers occupy too much space and consume too much power.
In order to address at least one of the aforementioned representative deficiencies in the art (or some other related shortcoming), various needs are apparent. A first need exists for a transmitter and receiver pair that are compact, for example as an integrated transceiver. A second need exists for a detector system that can differentiate between incoming and outgoing light. A third need exists for circuitry that processes an electrical signal imprinted or encoded both with incoming data and with outgoing data, with the processing revealing the incoming data. A fourth need exists for a laser that can produce outgoing optical signals while passing incoming optical signals for receipt by a detector. A fifth need exists for technology that can discriminate between light encoded with incoming data and light encoded with outgoing data. A sixth need exists for a method of processing optical signals (or corresponding electrical signals) imprinted with known information and unknown information in a manner that identifies the unknown information. A seventh need exists for a transceiver that can be mass produced with low-cost, that is small, and that provides low power consumption. An eighth need exists for a technology that can implement in electronics signal-separation functionality traditionally performed in the optical domain. A ninth need exists for signal processing that can address noise or signal degradation associated with stray light or with mixing optical signals in a transceiver. The foregoing discussion of needs in the art is intended to be representative rather than exhaustive. A technology addressing one or more such needs would benefit optical communications, for example via providing lower cost, better access to higher bandwidth, new applications, reduced size, lower power consumption, etc.